chemical changes 4 Flashcards

(46 cards)

1
Q

what is the PH scale

A

a measure of how acidic or alkaline a solution is
the lower the PH the more acidic
the higher the more alkaline

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2
Q

what is indicator

A

a dye that changes colour depending on weather it’s above or below a certain PH
some indicators contain a mixture of dys that means they gradually change colour over a broad range of PH

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3
Q

ways to measure PH

A

PH probe

measure electronically

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4
Q

what is an acid

A

a susbstance that forms aqueous solutions with PH of less than 7
Acids form H plus ions

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5
Q

what is a base

A

a substance with a PH level greater than 7

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6
Q

Base(alkali)

A

base that dissolves in water to form a solution with PH greater than 7
form OH minus ions

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7
Q

acid + base =

A

salt + water

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8
Q

H plus + OH minus =

A

H2O

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9
Q

what do reactions of strong acids and alkali help calculate

A

reactions of a strong acids and alkalis to calculate the concentration by titration

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10
Q

what PH does a neutral substance have

A

PH 7

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11
Q

what do strong acids do in water

A

ionise completely in water

all acid particles dissociate to release H plus ions

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12
Q

what do weak acids do in water

A

do not fully ionise

only a small proportion of particles dissociate to reales H plus ions

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13
Q

what kind of reaction is a weak acid

A

reversible reaction which sets up an equillibrium between the undissociated and dissociated ions.
lies on the left because only few H plus ions are released

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14
Q

what happens when the concentration of H plus ions increase

A

rate of reaction will be faster if strong acid

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15
Q

what is the PH of acid or alkali and what happens when the scale decreases

A

a measure of the concentration of H plus ions

for every decrease of 1 on the PH scale the concentration increases by a factor of 10

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16
Q

general rule when ion concentration changes

A

factor h plus ion concentration changes by 10-x (x is difference in PH)

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17
Q

what does acid strength tell you

A

what proportion of the acid molecules ionise in water

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18
Q

what is acid concentration

A

how much acid there is in a certain volume

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19
Q

metal oxides or metal hydroxide + acid =

20
Q

how you make a salt

21
Q

acid + metal carbonate =

A

salt + water + carbon dioxide

22
Q

what is the reactivity series

A

lists metals in order of their reactivity

23
Q

how is metal reactivity measured

A

how easily they lose there electrons and form positive ions

24
Q

acid + metal =

A

salt + hydrogen

25
how do you measure reactivity
react it with an acid | the speed of the reaction is indicated by the amount of hydrogen gas given off
26
metal + water =
metal hydroxide + hydrogen
27
what is a redox reaction
a reaction that separates a metal from it's oxide
28
Formation of metal ore =
Oxidation = gain of oxygen
29
extraction of metal ore =
Reduction = loss of oxygen
30
how is metal extracted with carbon
by reduction | ore is reduced as oxygen is removed from it and carbon gains oxygen so is oxidised
31
how are metals higher than carbon extracted
electrolysis
32
how are metals below carbon extracted
reduction using carbon
33
what is oxidation
a loss of electrons
34
what is reduction
a gain of electrons
35
OIL RIG
oxidation is loss reduction is gain
36
what are displacement reactions
involve one metal kicking another one out of it's compound
37
rule of displacement reaction
A more reactive metal will displace a less reactive metal
38
what gains the electrons and what loses the electrons during a displacement reaction
``` metal ion (reduced) metal atom (oxidised) ```
39
what is an ionic equation
only show particles that react and the products produced not the spectator ions
40
what and how does electrolysis do/work
an electric current is passed through an electrolyte positive ion in the electrolyte will move towards the cathode and gain electrons negative ions in the electrolyte will move towards the anode and loses electrons this creates a flow of charge through the electrolyte as the ions travel to the electrode
41
why electrolysis only works on molten ionic solids
ionic solid can't be electrolysised because ions are in a fixed position and don't move molten ionic compounds can be electrolysed because the ions can move freely positive ions are reduced to the element at the cathode negative ions are oxidised to the element at the anode
42
how is aluminium extracted using electrolysis
aluminium is extracted from the ore bauxite by electrolysis aluminium oxide has a very high melting temperature so it's mixed with cryolite to lower the melting point The molten mixture contains free ions the positive 3 plus AL ions are attracted to the negative electrode where they pick up three electrons and turn into neutral aluminium atoms the negative 2 minus O ions are attracted to the positive electrode where they each lose two electrons
43
overall equation of extracted aluminium
aluminium oxide = aluminium + oxygen
44
what do half equations show
show the reactions at the electrodes.
45
electrolysis of aqueous solutions what else is produced
as well as the ions produced from the compound there will be hydrogen ions and hydroxide ions from the water. at the cathode if the hydrogen ion is less reactive than the metal hydrogen gas is formed otherwise the metal ion coats the cathode at the anode if hydroxide ions are present, molecules of chlorine, bromine or iodine will be formed if no halide ions are present then the hydroxide ions are discharged and oxygen will be formed
46
reactivity series
``` potassium k sodium Na lithium Li calcium Ca magnesium Mg carbon C zinc Zn iron Fe hydrogen H copper Cu ```